Carburetor



Dec. 27, 1966 R. J. SMITH ETAL 3,294,374

GARBURETOR Filed Sept. 29, 1964 I5 Sheets-$heet 1 INVENTORS ROBERT J. SMITH OJJN J. EICKMANN AGENT 1966 R. J. SMITH ETAL CARBURETOR 5 Sheets-Sheet 2 Filed Sept. 29, 1964 INVENTORS ROBERT J. SMITH OLIN J. EICKANN 7/ AGENT United States Patent 3,294,374 CARBURETKUR Robert J. Smith, Florissant, and @lin .l'. Eickmann, Normandy, Mm, assignors to ACF industries llncorporated, New York, N.Y., a corporation of New Jersey Filed Sept. 29, 1964, Ser. No. 4%,000 20 Claims. (Cl. 2611-23) This invention relates to an improvement in multi-stage, multi-barrel carburetors, and particularly to a carburetor of this type of simplified construction but improved performance in the part-throttle to full-throttle engine operating range, especially at low normal engine operating temperatures.

Multistage carburetors are those which have a plurality of fuel and air mixture passages leading to the intake manifold of an engine. At least one of the mixture conduits, called a primary, is used to supply the fuel mixture to the engine during starting and from low to normal driving speeds under light loads. One or more other mixture conduits, called a secondary, becomes operative when a certain throttle opening is reached by the throttle in the primary conduit to provide more fuel and air to the engine for higher speeds or for greater loads at low speeds. Such a multi-barrel, multistage carburetor is shown and described in U.S. Patent 3,030,085 to L. B. Read.

For the starting of a cold engine using a carburetor of the type disclosed in the above cited patent, the present practice is to control the primary conduits with an automatic choke valve and to use a secondary throttle lockout to hold the secondary conduits out of operation, until the choke valve fully opens, as described and shown in the above Read patent.

This described operation of carburetors of this type is satisfactory for engines up to a certain engine size. However, with greater engine sizes (cubic inch displacement), full engine potential is only realized With much larger secondaries, of much greater flow capacity, which secondaries come into operation at lower engine speeds. Large engines are thus at a disadvantage when using carburetors having the secondary lock-out feature, since with choke on, the maximum fiow capacity of the carburetor is restricted to the capacity of the primaries, and these primaries have neither the air flow, nor fuel flow capacity necessary to obtain anything like the full performance inherent in a large engine. As a consequence, the engine power is severely restricted after a cold start, when full power may be required under adverse conditions.

It is one of the objects of this invention to provide a two stage carburetor with an automatic choke in the first stage which Will give substantial full engine performance of both stages while the automatic choke is operative.

It is still another object of this invention to provide a multi-stage, rnulti-barrel carburetor in which the secondary lock-out feature can be eliminated, thereby simplifying construction.

It is also an object of this invention to provide a multi stage carburetor providing use of both stages during cold engine operation for optimum engine performance.

It is a further object of this invention to provide a multi-stage carburetor in which both stages are operative under thermostatic control while the engine is cold.

This invention is described below with respect to multistage, multi-barrel carburetors with a pair of primary mixture conduits or barrels and a pair of secondary mixture conduits or barrels, in which the primaries are controlled by a pair of connected throttles and the secondaries by a separate pair of connected throttles, although the invention is applicable as well to other types of carburetors such as a two-stage, two-barrel carburetor, for example. In the carburetor described below, separate pairs of throttles are operated sequentially. The primaries are preferably plain tubes having venturi restrictions and equipped with a choke valve and an automatic control to operate the choke valve. The secondaries also may be simple plain tube carburetors, with or without venturis and provided with an automatic air valve, located upstream of the fuel nozzles in the plain tubes of the sec ondaries. The improvement here disclosed eliminates the necessity for a secondary throttle lock-out operated by the automatic choke together with the described disadvantages, which results in loss of engine performance, as above explained. Accordingly, this invention provides means for modulating the operation of the automatic throttle for the secondary by temperature responsive means as hereinafter described in detail. Other objects and advantages of this invention will appear from the following detailed description which is in such clear, concise, and exact terms as will enable any person skilled in the art to make and use the same when taken in conjunction with the accompanying drawings, forming a part thereof, and in which:

FIG. 1 is a side elevational view schematically illustrating a multi-stage, multi-barrel carburetor constructed in accordance with the teachings of this invention;

FIG. 2 is a side elevation of the opposite side of the carburetor shown in FIG. 1;

FIG. 3 is a top plan view of the carburetor shown in FIGS. 1 and 2;

FIG. 4 is a transverse sectional view taken on the line 44- of FIG. 3 looking in the direction of the arrows;

FIG. 5 is a transverse sectional view of the bowl cover and air horn, as shown in FIG. 4, illustrating a modification of the structure shown in FIGS. 1-4 inclusive.

In this description the term velocity stage refers to a plain tube type of carburetor, in which the drop in air pressure causing fuel fiow from a fuel nozzle is created by a venturi-like action. This same effect, when produced by throttling the air flow anterior of the fuel nozzle by a .valve in the mixture conduit, will be termed air valve effect. Where this effect is produced by both a venturi like action and by throttling the air flow anterior of the fuel nozzle by a valve, the term combined effect will be used. The differences in the meanings of these terms are important because, although similar results are obtained by each of the above termed structures, there is a distinct difference in the efficiency of the separate effects in producing the desired fuel metering. For example, an entirely different action exists in the response of a nozzle in a velocity stage at low air flow rates from the response of a nozzle to air valve effect at low air fiow rates. This invention is concerned with the control of a device which produces the combined effect and at the same time responds automatically to supply air and fuel to suit the engine requirements over a wide range of engine speeds, at variable engine temperatures and ambient air temperatures.

.In the embodiment of the invention, FIGURES 1-4 show a carburetor of a multi-stage, multi-barrel type having a carburetor body 1 provided with flanges 2, by which the carburetor body is secured to a suitable mounting pad at the inlets of an intake manifold M of an engine E. Secured on the body 1 is a float bowl cover 7 which includes an air horn 8 formed integrally therewith. As shown in FIG. 3, this is a four barrel carburetor and has a pair of primary stages comprising a pair of mixture conduits or barrels l0 and 12, respectively. The secondary stage has a pair of mixture conduits, or barrels 13 and 15, respectively. The air horn has a central partition 5 shown in FIG. 3 dividing the air horn and separating the primary conduits 1t) and 12 from the secondary conduits 13 and 15. In this modification, each barrel has a velocity stage. Primary barrels 10 and 12 are identical and one description will be explanatory of both. Each of these barrels has a fuel nozzle 14 opening in a primary venturi 16. Each primary venturi 16 is in turn disposed coaxially within a main venturi 18 (FIGURE 4).

The secondary barrels 13 and 15 are also alike and similar to the primaries, so that a description of one secondary will serve for both. Each secondary barrel 13 has a fuel nozzle 17 in a primary venturi 19 which is coaxially mounted within a main venturi 21. The primary and secondary barrels and 13 have their fuel nozzles 14 and 17 respectively connected with a fuel bowl located at 22, while primary and secondary barrels 12 and have fuel nozzles connected with a fuel bowl located at 23. The fuel bowls and the several fuel circuits are as shown and described in the aforementioned Read Patent 3,030,085. These fuel bowls are both supplied with fuel from a single inlet connection 24 on the float bowl cover for a fuel line 25 coupled with connection 24 and connected to a fuel pump P delivering fuel to the carburetor from a fuel tank T as schematically shown in FIG. 3. Both primary barrels 10 and 12 are controlled respectively by separate throttle valves 26, such as shown in FIG. 4, which are mounted on a single throttle shaft 27. Both secondary barrels 13 and 15 similarly have separate manually controlled throttles 28, as shown in FIG. 4, both fixed to and operated by a single throttle shaft 29. Shafts 27 and 29 are rotatably mounted in the body of the carburetor 1.

One end of the throttle shaft 27 mounts a throttle lever 30 (FIG. 2) with an eye 31 for connection with a manually operated throttle linkage. On the lever 30, is a lug 34 with a threaded hole for the idle speed adjusting screw 33. The end of this screw 33 is disposed for contact on the surface of fast idle cam arm 36 of a lever 35 rotatable on its shaft 38. Opposite cam arm 36 is a weighted arm 40 of lever 35 to bias the lever 35 by gravity in a clockwise direction. Lever 35 is connected by link 41 to arm 44 fixed to a counter shaft 43 journaled through the body 1. Fixed to shaft 43 is a lever 46 (see FIGS. 3 and 4) which through link 49 and bracket 50 operate a choke valve 47, fixed to a choke shaft 48. Choke shaft 48 is journaled in the sides of the air horn 8 on the primary side and eccentrically mounts the choke valve 47 for rotational movement so that in a closed position choke valve 47 substantially closes the air horn on the primary side as shown by the position of the choke valve 47 in FIG. 4. The choke valve 47 thus controls the inlet to both primary barrels 10 and 12 for throttling the air flow at the inlet of each. Counter shaft 43 is rotated by the automatic choke control within the housing 53 (see FIGS. 1 and 3) which contains a thermostatic coil 52 and engine suction operated motor means consisting of a piston 54 within a cylinder 56 and connected to a linkage 58 fixed to shaft 43 within the choke housing 53. Cylinder 56 is closed at its lower end and joined by an air passage 60 to the primary side of the carburetor downstream of the throttles 26.

The secondary throttle shaft 29 is controlled by a linkage from the primary throttle shaft 27 as shown in FIG. I. This linkage includes an arm 55 fixed to primary throttle shaft 27 and connected by drag link 56 having a slotted lost-motion connection 61 with a lever 57 rotatable on secondary throttle shaft 29. A lug 58 on lever 57 is bent backwards in a direction to act as a wide open stop on lug 60 on the body casting 1. Since arm 55 starts from an overcenter position and 57 is slotted at 61, throttles 26 open ahead of throttles 28, and both sets of throttles reach wide open position simultaneously. There is no secondary lock-out feature as disclosed in the aforesaid Read patent, but otherwise the throttle system shown is the same.

In accordance with a feature of this invention as shown in FIGS. 3 and 4, the carburetor is provided with an air valve 64 eccentrically mounted on a throttle shaft 65 journaled in the air born 8 on the secondary side of the carburetor. Air valve 64 substantially closes the second- 4 ary side of air horn 8 from partition 5 and controls the air flow at the inlet of the secondary barrels 13 and 15. Air valve 64 is an unbalanced air flow responsive type of valve similar to the choke valve 47. A lever arm 66 is fixed to the valve 64 on the shaft 65. A coil spring 68 is fixed under compression with one end fixed in the bracket 50 oif-center of choke shaft 48 and its opposite end 69 fixed in the lever arm 66 off-center of shaft 65. Coil spring 68 is normally a tightly wound straight coil spring, but when placed under compression, as shown in FIG. 4, it is deformed to an arcuate shape which opens the pitch of the coils at the outside of the arc. Spring 68 biases valve 64 in a closed direction against the fiow of air through the secondary side of the carburetor on the unbalanced valve 64.

As is well known, and as pointed out in the above cited Read patent, the amount of opening of the choke valve 47 is controlled during cold engine operation by the thermostatic spring coil 52 in housing 53. Coil 52 has one end fixed and the other end 44 abutting a lever arm 72 of lever 58 on shaft 43. Shaft 43, as shown in FIGS. 3 and 4, is connected for movement with choke shaft 48 through lever 46 and link 49. When the engine is cold at a temperature below the middle 70s R, the end 44 of the thermostatic coil spring 52 moves clockwise, as seen in FIG. 1, and biases the choke valve 47 through the described linkage to the closed position shown in FIG. 4. This closed position of the choke valve is substantially retained while the engine is being cranked but upon firing and starting of the engine, the manifold vacuum actuated piston 54 within the choke housing 53 opens the choke to a small degree to permit sufficient air flow to the engine. This positioning of the choke by the piston is against the bias of the thermostatic coil spring 52 and is only to a degree to reduce the depression or choking effect downstream of the valve 47. This opening of the choke upon the starting of the engine leans down the rich cranking mixture but still retains a sutficiently rich cold engine idle mixture. If the engine is driven away at this point, or speeded up, the additional flow of air through the carburetor to the engine will open the choke valve to a greater degree against the bias of the choke coil. As the engine warms up to normal operating temperatures, however, the choke coil relaxes completely and the coil end 44 will move counter-clockwise as viewed in FIG. 1, out of the path of movement of lever arm 72. At this time, air fiow through the carburetor will maintain choke valve 47 in the vertical position shown in FIG. 1, where it in no way effects the operation of the carburetor, until the temperature of the engine falls below the middle 70s, and coil end 44 moves back into the path of movement of lever arm 72.

In the range of movement of the choke valve 47 from closed to partly open position and during engine warmup operation, it operates strictly as an air valve to produce restriction to air flow through the primary barrels 10 and 12. This results in a pressure depression or partial vacuum in the barrels downstream of valve 47 in the region of nozzles 4, which draws fuel through the nozzles into the mixture of passages 10 and 12. When valve 47 reaches substantially full open position, it has no air valve effect and the primary barrels 10 and 12 function as single velocity stage carburetors in which air flow through the venturis 14 draws fuel through nozzles 14 into the primary barrels.

The action of air valve 64 is somewhat similar to that of the choke valve 47. In the range of movement of valve 64 between closed and partly open positions, in response to engine suction and the degree of opening of secondary throttles 23, valve 64 produces strictly an air valve effect against the bias of spring 68. When fully open, air valve 64 has no air valve effect and the secondary barrels function as single velocity stage carburetors.

In accordance with the invention, valve 64 is connected to choke valve 47 whereby its action is modified by the position of choke valve 47 between closed and wide open position of the choke valve and is thus also responsive to engine temperature below the middle 70s F.

When the engine is warm and at a temperature above the middle 70s F., the choke valve 47 is maintained by the tensioned spring 68 in the vertical position shown in FIGURE 1 due to the turning moment of spring end 70 on the bracket lever 50. Simultaneously, spring 68 holds the air valve throttle 64 closed, as shown in FIGURE 4, as long as the secondary throttles 28 remain closed. With the secondary throttles 28 open, air valve throttle 64 will open against the bias of spring 68 an amount determined by the flow of air through the secondary side of the carburetor. As valve 64 opens toward the wide open position, shown in FIGURE 1, spring 68 will be bent to decrease its radius and thus progressively increase the force on the valve lever 66. Between the closed and open position of valve 64, the lever arm 66 moves between its position at 66a and that at 66 and the effective lever arm of lever 66 becomes increasingly shorter and may thus compensate wholly or in part for the increased force of spring 68 as valve 64 opens. Any desired closing torque on air valve 64 may be obtained by determining the proper strength of spring 68 as related to the length of arm 66. Depending upon the angular position of arm 66 about the axis of shaft 65, the torque can also be varied to provide an increasing or decreasing closing torque on valve 64 as air flow moves it toward its open position.

Also, in accordance with the invention, between the closed and open positions of the choke valve 47, resistance imposed by the arcuate spring 68 is a variable one depending on choke valve position and due to its manner of connection with the choke valve 47. Thus, the resistance of spring 68 to opening movement of valve 64, when the choke valve is closed, or partly open during cold engine operation, is greater than its resistance to opening movement of valve 64, when the choke valve 47 is wide open when the engine is warm. As a consequence, the degree of air valve effect or throttling by air valve 64 is greater when the choke valve 47 is closed, than when the choke valve is open. Thus, the greater the degree of throttling produced by air valve 64, the greater the drop in pressure downstream of valve 64 and the greater the rate of fuel flow from nozzles 17 with respect to the rate of air flow through the barrels 13 and 15 thus making the mixture richer for cold engine operation. Operation of a cold engine utilizing both primary and secondary barrels is made possible due to this intensification of air valve effect in the secondary barrels by the indirect cold temperature control imposed on the spring 68 by the automatic choke control in the primary barrels.

Spring 68 is not a compression spring in the general sense of the word. The bias of spring 68 is due more to its force bending moment. Spring 68 will affect the operation of the thermostatic choke coil 52 during cold engine operation as determined by the change in the effective lever arm of bracket 50 about the axis of the choke shaft 48, but this may be compensated for by calibration of the choke mechanism for optimum operation of the choke valve 47. That is, the automatic choke mechanism including its choke coil 52 and choke valve 47 may be calibrated to suit the primaries and their operation. The arrangement of spring 63 lessens the opening of valve 64 due to air flow, during cold engine operation, an amount to provide a choking effect in the secondary conduits resulting in an enriched mixture from the secondary side of the carburetor. Thus, during cold engine operation and at wide open throttles, the need for a secondary lock-out for the secondary throttles 28 is eliminated.

This invention permits the secondary conduits to come into operation within a low speed range of engine operation at wide open throttles whether the engine is cold or is fully warmed up. The resulting advantage is definitely significant in the warmup stages of engine operation, because with the secondaries coming in early, full engine power is available, while the engine is still cold or in the warmup state.

Although the invention has been described in combination with an automatically operated choke valve 47, it is clear that the invention is also applicable to carburetor using a manually operated choke and in the same manner and with the same results as described above, since the choke valve 47 can be positioned in any manner to modify the action of the valve biasing Spring 68.

A slightly modified version of the above described control is shown in FIG. 5. This modification substitutes a bimetal arm 66' for the arm 66. Otherwise, the embodiment in FIG. 5 operates in the same way as that above described, Bimetal lever 66 wraps around shaft and through valve 64, so that the free end 67 of lever 66' is fixed to the top surface of valve 64 to bias it closed. The other end of lever 66' is twisted and has an eye to receive the end 69 of the spring 68.

The operation of the form shown in FIG. 5 is substantially the same as that above explained except that thermostat compensates for ambient air temperature changes by variation in the action of spring bias on the automatic air valve 64 at the entrance of the secondary conduits. As air temperature drops, arm 66' moves to the right in FIG. 5 increasing the bending or buckling in spring 68, which increases the bias of the spring 68 to increase the degree of throttling or air valve effect of valve 64. This increase in throttling or air valve effect is operable throughout the range of action of the valve 64. The air temperature increases, the reverse operation occurs and arm 66 moves to the left with respect to the valve 64. This movement decreases the bias of spring 68 and decreases the throttling or air valve effect of the valve 64 which results in leaning out the air-to-fuel mixture slightly under warm conditions.

Actually, the mixture ratio need not be enriched or leaned out by the thermostat action of the arm 66'. The movement of this arm 66 may be sufficient by calibration to merely maintain the fuel ratio constant regardless of temperature change. Since cold air is more dense than warm air it results in a leaner mixture unless the rate of fuel flow is increased by the throttling action or air valve effect of air valve 64. Thermostat 66 tends to compensate by increasing the throttling effect and thereby slightly increasing the rate of fuel flow to air flow. On the other hand, as temperature increases, air density decreases, and the air fuel mixture tends to become richer unless the rate of fluel flow is decreased slightly. Thermostat 66 tends to decrease air valve effect slightly as temperature increases so as to compensate for the decrease in density as air temperature increases.

We claim:

1. A multistage carburetor for an internal combustion engine comprising a body structure having a primary mixture conduit and a secondary mixture conduit for the flow of an air and fuel mixture therethrough to said engine, means including a primary nOZZle for providing fuel flow into said primary conduit and a secondary nozzle for providing fuel flow into said secondary conduit,

manually operable means including a primary throttle and a secondary throttle movably mounted respectively within said primary and secondary conduits and downstream respectively of said nozzles for controlling the flow of air-fuel mixture therethrough, a control valve within said secondary conduit upstream of said secondary nozzle therein, means mounting said control valve for movement from a position closing said secondary conduit toward an open position by air flow through said secondary conduit, means connected to said control valve normally biasing said control valve against said air flow toward said closed position, and temperature responsive means connected to said control valve biasing means to modify said control valve biasing means in response to engine temperature.

2. A multistage carburetor for an internal combustion engine comprising a body structure having a primary mixture conduit and a secondary mixture conduit for the flow of an air and fuel mixture therethrough to said engine, means including a primary nozzle for providing fuel flow into said primary conduit and a secondary nozzle for providing fuel flow into said secondary conduit, manually operable means including a primary throttle and a secondary throttle movably mounted respectively within said primary and secondary conduits and downstream respectively of said nozzles for controlling the flow of air-fuel mixture therethrough, a control valve within said secondary conduit upstream of said secondary nozzle therein, means eccentrically mounting said control valve for movement from a position closing said secondary conduit to- Ward an open position by air fiow through said secondary conduit, a spring connected to said control valve normally biasing said control valve against said air flow toward said closed position, and engine temperature responsive means connected to said spring to modify the action of said spring in response to engine temperatures.

3. A multistage carburetor for an internal combustion engine comprising a body structure having a primary mixture conduit and a secondary mixture conduit for the flow of an air and fuel mixture therethrough to said engine, means including a primary nozzle for providing fuel flow into said primary conduit and a secondary nozzle for providing fuel flow into said secondary conduit, manually operable means including a primary throttle and a secondary throttle movably mounted respectively within said primary and secondary conduits and downstream respectively of said nozzles for controlling the flow of air-fuel mixture therethrough, a control valve within said secondary conduit upstream of said secondary nozzle therein to provide a variable restriction to air flow through said secondary conduit, means eccentrically mounting said control valve for movement from a position closing said secondary conduit toward an open position by air flow through said secondary conduit, a spring connected to said control valve normally biasing said control valve against said air flow toward said closed position, a choke valve movably mounted within said primary conduit upstream of said primary nozzle therein for restricting air flow through said primary conduit, and engine temperature responsive means connected to said spring and choke valve to vary the position of said valves in response to changes in engine temperature.

4. The invention of claim 4, wherein said engine temperature responsive means includes a heat responsive coil and connecting means including said biasing spring operatively joining said heat responsive coil to said choke and control valves.

5. A multistage carburetor for an internal combustion engine comprising a body structure having a primary mixture conduit and a secondary mixture conduit for the fiow of an air and fuel mixture therethrough to said engine, means including a primary nozzle for providing fuel flow into said primary conduit and a secondary nozzle for providing fuel flow into said secondary conduit, manually operable means including a primary throttle and a secondary throttle movably mounted respectively within said primary and secondary conduits and downstream respectively of said nozzles for controlling the flow of air-fuel mixture therethrough, a control valve within said secondary conduit upstream of said secondary nozzle therein, means mounting said control valve for movement from a position closing said secondary conduit toward an open position by air flow through said secondary conduit, means connected to said control valve normally biasing said control valve against said air flow toward said closed position, a choke valve rotatably mounted within said primary conduit for restricting air fiow through said primary conduit, means connecting said control valve biasing means to said choke valve whereby movement of said choke valve modifies the action of said biasing means on said control valve.

6. The invention of claim wherein said control valve biasing means includes a spring structure connected at ell) one end to said control valve and connected at the other end thereof to said choke valve whereby movement of said choke valve modifies the bias of said spring on said control valve.

7. The invention of claim 6 including a thermostatic coil adapted to be responsive to engine temperature, and means operatively connecting said thermostatic coil to said choke valve to bias said choke and control valve toward closed positions respectively when said engine temperature is below a predetermined value.

8. The invention of claim 6 wherein said spring structure includes a heat sensitive link to modify the biasing effect of said spring structure in response to the temperature of air entering said carburetor.

9. A multistage carburetor for an internal combustion engine comprising a body structure having a primary mixture conduit and a secondary mixture conduit for the flow of an air and fuel mixture therethrough to said engine, means including a primary nozzle for providing fuel flow into said primary conduit and a secondary nozzle for providing fuel flow into said secondary conduit, manually operable means including a primary throttle and a secondary throttle movably mounted respectively within said primary and secondary conduits and downstream respectively of said nozzles for controlling the flow of air-fuel mixture therethrough, a control valve within said secondary conduit upstream of said nozzle therein to provide a variable restriction of air flow through said secondary conduit, a valve shaft journaled in said body structure and eccentrically mounting said control valve for movement from a position closing said secondary conduit toward an open position by air flow through said secondary conduit, a spring connected to said control valve normally biasing said control valve against said air fiow toward said closed position, a choke valve within said primary conduit upstream of said nozzle therein, a choke shaft journaled in said body structure and eccentrically mounting said choke valve for movement from a position closing said primary conduit toward an open position by air flow through said primary conduit, said spring having one end connected to said control valve and the other end thereof to said choke valve at a point spaced from the axis of said choke shaft whereby the distance between said spring ends is lengthened when said choke valve is moved from a closed to open position to reduce said spring bias on said control valve.

10. The invention of claim 9 including engine temperature responsive means to vary the position of said choke valve in response to engine temperature.

11. The invention of claim 9 including a thermostatic coil adapted to be responsive to engine temperature, and means operatively connecting said thermostatic coil to said choke valve to bias said choke and control valve toward closed positions respectively when said engine temperature is below a predetermined valve.

12. A multistage carburetor for an internal combustion engine comprising a body structure having a pair of primary mixture conduits and a pair of secondary mixture conduits for the flow of an air and fuel mixture therethrough to said engine, means including a different primary nozzle for providing fuel flow into each of said pri mary conduits, means including a different secondary nozzle for providing fuel flow into each of said secondary conduits, manually operable primary throttles and secondary throttles movably mounted respectively within each of said primary and secondary conduits and downstream respectively of said nozzles for controlling the flow of air-fuel mixture therethrough, control valve structure within said secondary conduits upstream of said respective nozzles therein, means mounting said control valve structure for movement from a position closing said secondary conduits toward an open position in response to air flow through said secondary conduits, means connected to said control valve structure normally biasing said control valve structure against said air flow toward said closed position to provide a pressure drop across said air valve structure, and temperature responsive means connected to said control valve biasing means to modify said control valve biasing means in response to engine temperature.

13. The invention of claim 12 wherein said control valve structure biasing means includes temperature responsive structure within said secondary mixture conduits to modify the biasing effect of said control valve biasing means in response to the temperature of air entering said carburetor.

14. A multistage carburetor for an internal combustion engine comprising a body structure having a pair of primary mixture conduits and a pair of secondary mixture conduits for the flow of an air and fuel mixture therethrough to said engine said conduits each having a venturi restriction between the ends thereof, means including a different primary nozzle for providing fuel flow into the venturi restriction within each of said primary conduits, means including a different secondary nozzle for providing fuel flow into the venturi restriction within each of said secondary conduits, manually operable primary throttles and secondary throttles movably mounted respectively within each of said primary and secondary conduits and downstream respectively of said venturi restrictions for controlling the flow of air-fuel mixture therethrough, control valve structure within said secondary conduits upstream of said respective venturi restrictions therein to provide a variable restriction to air flow through said secondary conduits, means mounting said control valve structure movement from a position closing said secondary conduits toward an open position in response to air flow through said secondary conduits, spring means connected to said control valve structure normally biasing said control valve structure against said air flow toward said closed position to provide a pressure drop across said air valve structure, a choke valve movably mounted Within said primary conduits upstream of said primary venturis therein for restricting air flow through said primary conduits, and engine temperature reseponsive means connected to said choke valve and spring means to control the operation thereof in response to engine temperature.

15. The invention of claim 14 wherein said engine temperature responsive means includes a heat responsive coil and connecting means including said biasing spring means operatively joining said heat responsive coil to said choke valve and said control valve structure.

16. A multistage carburetor for an internal combustion engine comprising a body structure having a pair of primary mixture conduits and a pair of secondary mixture conduits for the flow of an air and fuel mixture therethrough to said engine, means including a different primary nozzle for providing fuel flow into each of said primary conduits, means including a different secondary nozzle for providing fuel flow into each of said secondary conduits, manually operable primary throttles and secondary throttles movably mounted respectively within each of said primary and secondary conduits and downstream respectively of said nozzles for controlling the flow of air-fuel mixture therethrough, control valve structure within said secondary conduits upstream of said respective nozzles therein, means eccentrically mounting said control valve structure for rotational movement from a position closing said secondary conduits toward an open position in response to air flow through said secondary conduits, .a coil spring connected to said control valve structure normally biasing said control valve structure against said air flow toward said closed position to provide a pressure drop across said air valve structure, a choke valve positioned across said primary conduits upstream of said primary nozzles, a choke valve shaft journaled in said body structure and eccentrically mounting said choke valve for movement from a position clos ing said primary conduits toward an open position by air flow through said primary conduits, said coil spring having one end connected to said control valve structure and the other end thereof to said choke valve where-by movement of said choke valve modifies the bias of said coil spring.

17. The invention of claim 16 including a thermostatic coil adapted to be responsive to engine temperature, and means operatively connecting said thermostatic coil to said choke valve to bias said. choke valve and said control valve structure toward closed positions respectively when said engine temperature is below a predetermined value.

18. A multistage carburetor for an internal combustion engine comprising a body structure having a pair of primary mixture conduits and a pair of secondary mixture conduits for the flow of an air and fuel mixture therethrough to said engine, means including a different primary nozzle for providing fuel flow into each of said primary conduits, means including a different secondary nozzle for providing fuel flow into each of said secondary conduits, manually operable primary throttles and secondary throttles movably mounted respectively Within each of said primary and secondary conduits and downstream respectively of said nozzles for controlling the flow of air-fuel mixture therethrough, control valve structure within said secondary conduits upstream of said respective nozzles therein, means eccentrically mounting said control valve structure for rotational movement from a position closing said secondary conduits toward an open position in response to air flow through said secondary conduits, a coil spring connected to said control valve structure normally biasing said control valve structure against said air flow toward said closed position to provide a pressure drop across said air valve structure, a choke valve within said primary conduit upstream of said nozzle therein, a choke shaft journaled in said body structure and eccentrically mounting said choke valve for movement from a position closing said primary conduit toward an open position by air flow through said primary conduit, said spring having one end connected to said control valve structure and the other end thereof to said choke valve at a point spaced from the axis of said choke shaft whereby the distance between said spring ends is lengthened when said choked valve is moved from a closed to open position to reduce said spring bias on said control valve structure.

19. The invention of claim 18 including a thermostatic coil adapted to be responsive to engine temperature, and means operatively connecting said thermostatic coil to said choke valve to bias said choke valve and said control valve structure toward closed positions respectively when said engine temperature is below a predetermined value.

20. The invention of claim 18, wherein one of said coil spring ends is connected to a temperature responsive link to modify the biasing effect of said coil spring in response to the temperature of air entering said carburetor.

References Cited by the Examiner UNITED STATES PATENTS 2,420,925 5/1947 Wirth. 2,640,472 6/ 1953 Bicknell 123-127 2,832,576 4/ 1958 Henning. 2,995,351 18/ 1961' Brown et al. 3,05 3,240 9/ 1962 Mick. 3,186,691 6/ 1965 Manning. 123127 X HARRY B. THORNTON, Primary Examiner.

RONALD R. WEAVER, Examiner. 

1. A MULTISTAGE CARBURETOR FOR AN INTERNAL COMBUSTION ENGINE COMPRISING A BODY STRUCTURE HAVING A PRIMARY MICING CONDUIT AND A SECONDARY MIXTURE CONDUIT FOR THE FLOW OF AN AIR AND FUEL MIXTURE THERETHROUGH TO SAID ENGINE, MEANS INCLUDING A PRIMARY NOZZLE FOR PROVING FUEL FLOW INTO SAID PRIMARY CONDUIT AND A SECONDARY NOZZLE FOR PROVIDING FUEL FLOW INTO SAID SECONDARY CONDUIT, MANUALLY OPERABLE MEANS INCLUDING A PRIMARY THROTTLE AND A SECONDARY THROTTLE MOVABLY MOUNTED RESPECTIVELY WITHIN SAID PRIMARY AND SECONDARY CONDUITS AND DOWNSTREAM RESPECTIVELY OF SAID NOZZLES FOR CONTROLLING THE FLOW OF AIR-FUEL MIXTURE THERETHROUGH, A CONTROL VALVE WITHIN SAID SECONDARY CONDUIT UPSTREAM OF SAID SECONDARY NOZLE THEREIN, MEANS MOUNTING SAID CONTROL VALVE FOR MOVEMENT FROM A POSITION CLOSING SAID SECONDARY CONDUIT TOWARD AN OPEN POSITION BY AIR FLOW THROUGH SAID SECONDARY CONDUIT, MEANS CONNECTED TO SAID CONTROL VALVE NORMALLY BIASING SAID CONTROL VALVE AGAINST SAID AIR FLOW TOWARD SAID CLOSED POSITION, AND TEMPERATURE RESPONSIVE MEANS CONNECTED TO SAID CONTROL VALVE BIASING MEANS TO MODIFY SAID CONTROL VALVE BIASING MEANS IN RESPONSE TO ENGINE TEMPERATURE. 